Method for selectively producing propylene by catalytically cracking an olefinic hydrocarbon feedstock

ABSTRACT

The invention provides a method for converting an olefinic hydrocarbon feedstock to propylene comprising: contacting a hydrocarbon feedstock under catalytic cracking conditions with a catalyst comprising a catalyst selected from the group consisting of SAPO catalysts, MeAPO catalysts, MeASPO catalysts, ELAPO catalysts, ELASPO catalysts, rare earth exchanged catalysts from any of the preceding groups, and mixtures thereof, under cracking conditions to selectively produce propylene. The invention further provides a method for stabilizing a catalyst to steam from the foregoing group by ion exchange with a rare earth metal. A catalyst has enhanced stability as used herein when treated with a rare earth metal or metals in a concentration effective to provide a catalyst which exhibits a higher conversion of a hydrocarbon feedstock to propylene than does an equal quantity of an untreated sample of the same catalyst under the same conditions following exposure of each catalyst to steam for a period of at least 10 hours.

FIELD OF THE INVENTION

[0001] The invention relates to catalytic cracking of hydrocarbons.Particularly the invention relates to a method providing improvedselectivity for cracking hydrocarbon feedstocks to propylene bycontacting the hydrocarbon under cracking conditions with a catalystselected from the non-zeolitic molecular sieves consisting ofsilicoaluminophosphates (“SAPO”), metal aluminophosphates (“MeAPO”),metal aluminosilicophoshates (“MeASPO”), elemental aluminophosphates(“ElAPO”) and elemental aluminosilcophosphates (“ElASPO”) where themetals include divalent Co, Fe, Mg, Mn, and Zn and trivalent Fe and theelements include Li, Be, B, Ga, Ge, As, and Ti.

BACKGROUND OF THE INVENTION

[0002] Thermal and catalytic conversion of hydrocarbons to olefins is animportant industrial process producing millions of pounds of olefinseach year. Because of the large volume of production, small improvementsin operating efficiency translate into significant profits. Catalystsplay an important role in more selective conversion of hydrocarbons toolefins.

[0003] While important catalysts are found among the natural andsynthetic zeolites, it has also been recognized that non-zeoliticmolecular sieves such as silicoaluminophosphates (SAPO) including thosedescribed in U.S. Pat. No. 4,440,871 also provide excellent catalystsfor cracking to selectively produce light hydrocarbons and olefins. TheSAPO molecular sieve has a network of AlO₄, SiO₄, and PO₄ tetrahedralinked by oxygen atoms. The negative charge in the network is balancedby the inclusion of exchangeable protons or cations such as alkali oralkaline earth metal ions. The interstitial spaces or channels formed bythe crystalline network enables SAPOs to be used as molecular sieves inseparation processes and in catalysis. There are a large number of knownSAPO structures. The synthesis and catalytic activity of the SAPOcatalysts are disclosed in U.S. Pat. No. 4,440,871.

[0004] In other crystalline microporous solids belonging to the class ofaluminophosphates the framework is normally neutral (Al (III):P (V)atomic ratio=1). This framework can be made negative and thereby givesthese materials advantageous properties such as adsorption, cationexchange or catalytic activity by replacing P(V) or the pair Al (III),P(V) with a tetravalent element such as silicon, converting to theclosely related SAPO structure discussed above, or by replacing Al (III)with a metal, especially a divalent metal such as zinc or cobalt, thematerials obtained being denoted by the acronym MeAPO where Me is themetal, or else by combining these two types of substitution, thematerials obtained being denoted by the acronym MeAPSO. A group of suchmaterials is described in U.S. Pat. No. 5,675,050.

[0005] In the International Application WO 91/18851 the exchange ofcations to provide Lewis acid sites in zeolite and SAPO catalyticstructures in isomerization catalysts is disclosed. SAPO-11 is disclosedas being particularly effective in this system. The application focuseson skeletal isomerization of n-olefins. There is no teaching of enhancedselectivity or stability under catalytic cracking conditions. Nor isthere any discussion of increased stability in rare earth exchangedSAPO.

[0006] SAPO catalysts mixed with zeolites (including rare earthexchanged zeolites) are known to be useful in cracking of gasoils (U.S.Pat. No. 5,318,696). U.S. Pat. Nos. 5,456,821 and 5,366,948 describecracking catalysts with enhanced propylene selectivity which aremixtures of phosphorus treated zeolites with a second catalyst which maybe a SAPO or a rare earth exchanged zeolite. Rare earth treated zeolitecatalysts useful in catalytic cracking are disclosed in U.S. Pat. Nos.5,380,690, 5,358,918, 5,326,465, 5232,675 and 4,980,053. The use of SAPOcatalysts for cracking crude oil feed or “carbon-hydrogen fragmentationcompounds” (materials with 5 or less carbons) is disclosed in U.S. Pat.No. 4,666,875 and 4,842,714 (SAPO-37 preferred for cracking gas oils).Although these patents disclose the use of rare earth exchanged SAPOcatalysts, they state: “At present the presence of rare earth cationswith the SAPO molecular sieves has not been observed to be beneficial tothe activity of the SAPO component. The exact nature of the relationshipof multi-valent cations and SAPO catalysts is not clearly understood atpresent, although in some instances their presence may be beneficial.”(U.S. Pat. No. 4,666,875 at Col. 4 Lines 39-44, U.S. Pat. No. 4,842,714Col. 11, Lines 29-34.)

[0007] The art has not previously recognized the highly selectiveconversion of hydrocarbon, especially naphtha feedstocks to propylenepromoted by SAPO and related catalysts nor the improved stabilityobtained by rare earth exchanging such catalysts.

SUMMARY OF THE INVENTION

[0008] The invention provides a method for converting an olefinichydrocarbon feedstock to propylene comprising: contacting a hydrocarbonfeedstock under catalytic cracking conditions with a catalyst comprisinga nonzeolitic catalyst selected from the group consisting of SAPOcatalysts, MeAPO catalysts, MeASPO catalysts, ElAPO catalysts, ElASPOcatalysts, rare earth exchanged catalysts from any of the precedinggroups, and mixtures thereof, under cracking conditions to selectivelyproduce propylene. Preferably the method is carried out to producepropylene in a propylene to ethylene ratio of at least 4:1 and apropylene to butylene ration of at least 2:1. The invention furtherprovides an method for stabilizing a catalyst from the foregoing groupby ion exchange with a rare earth metal. A catalyst has enhancedstability as used herein when treated with a rare earth metal or metalsin a concentration effective to provide a catalyst which exhibits ahigher conversion of a hydrocarbon feedstock to propylene than does anequal quantity of an untreated sample of the same catalyst under thesame conditions following exposure of each catalyst to steam for aperiod of at least 10 hours. The invention also provides an improvementin methods for catalytic cracking of an olefinic hydrocarbon feedstockto produce a light olefin containing product wherein it is desired toimprove the propylene content of the product mixture. The improvementcomprises mixing a catalyst selected from the non zeolitic catalystgroup consisting of SAPO catalysts, MeAPO catalysts, MeASPO catalysts,ElAPO catalysts and ElASPO catalysts with a second cracking catalyst ina quantity sufficient to increase propylene content in the light olefinproduct while decreasing either ethylene or butylene when the productcomposition obtained with the mixed catalyst is compared to the productcomposition obtained with the second catalyst alone under the samereaction conditions.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The silicoaluminophosphate (SAPO) catalysts useful in the presentinvention have a three-dimensional microporous crystal frameworkstructure of PO₂ ⁺, AlO₂ ⁻ and SiO₂ tetrahedral units, and whoseessential empirical chemical composition on an anhydrous basis is: mR:(Si[x]Al[y]P[z])O[2] wherein “R” represents at least one organictemplating agent present in the intracrystalline pore system: “m”represents the moles of “R” present per mole of (Si[x]Al[y]P[z])O2 andhas a value of from zero to 0.3, the maximum value in each casedepending upon the molecular dimensions of the templating agent and theavailable void volume of the pore system of the particularsilicoaluminophosphate species involved, “x”, “y” and “z” represent themole fractions of silicon, aluminum and phosphorus, respectively,present as tetrahedral oxides, representing the following values for“x”, “y” and “z”. Mole Fraction x y z 0.01 0.47 0.52 0.94 0.01 0.05 0.980.01 0 01 0.39 0.60 0.01 0.01 0.60 0.39

[0010] When synthesized in accordance with the process disclosed in U.S.Pat. No. 4,440,871, the minimum value of “m” in the formula above is0.02. In a preferred sub-class of the SAPOs useful in this invention,the values of “x”, “y” and “z” in the formula above are set out in thefollowing table: Mole Fraction x y z 0.02 0.49 0.49 0.25 0.37 0.38 0.250.48 0.27 0.13 0.60 0.27 0.02 0.60 0.38

[0011] Preferred SAPO catalysts include SAPO-11, SAPO-17, SAPO-31,SAPO-34, SAPO-35, SAPO-41, and SAPO-44.

[0012] The catalysts suitable for use in the present invention include,in addition to the SAPO catalysts, the metal integratedaluminophosphates (MeAPO and ELAPO) and metal integratedsilicoaluminophosphates (MeAPSO and ElAPSO). The MeAPO, MeAPSO, ElAPO,and ElAPSO families have additional elements included in theirframework. For example, Me represents the elements Co, Fe, Mg, Mn, orZn, and El represents the elements Li, Be, Ga, Ge, As, or Ti. Preferredcatalysts include MeAPO-11, MeAPO-31, MeAPO-41, MeAPSO-11, MeAPSO-31,and MeAPSO-41, MeAPSO-46, ElAPO-11, ElAPO-31, ElAPO-41, ElAPSO-11,ElAPSO-31, and ElAPSO-41.

[0013] The non-zeolitic SAPO, MeAPO, MeAPSO, ElAPO and ElAPSO classes ofmicroporus materials are further described in the “Atlas of ZeoliteStructure Types” by W. M. Meier, D. H. Olson and C. Baerlocher (4th ed.,Butterworths/Intl. Zeolite Assoc. (1996) and “Introduction to ZeoliteScience and Practice”, H. Van Bekkum, E. M. Flanigen and J. C. JansenEds., Elsevier, New York, (1991).).

[0014] The selected catalysts may also include cations selected from thegroup consisting of cations of Group IIA, Group IIIA, Groups IIIB toVIIBB and rare earth cations selected from the group consisting ofcerium, lanthanum, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium and mixtures thereof.

[0015] Preferred olefinic hydrocarbon feedstocks are nathphas in theboiling range of 18° to 220° C. (65° F. to 430° F.). The naphthas may bethermally cracked naphthas or catalytically cracked naphthas. The feedshould contain from at least 10 wt % to about 70 wt % olefins,preferably 20 wt % to 70 wt %, and may also include naphthenes andaromatics. The naphthas may contain paraffins in the range of 5 wt % to35 wt %, preferably 10 wt % to 30 wt %, most preferably 10 wt % to 25 wt%. For example, the naphtha may be derived from fluid catalytic cracking(“FCC”) of gas oils and resids, or from delayed or fluid coking ofresids. The preferred naphtha streams are derived from FCC gas oils orresids which are typically rich in olefins and diolefins and relativelylean in paraffins.

[0016] Catalytic cracking conditions means a catalyst contactingtemperature in the range of about 400° C. to 750° C., more preferably inthe range of 450° C. to 700° C., most preferably in the range of 500° C.to 650° C. The catalyst contacting process is preferably carried out ata weight hourly space velocity (WHSV) in the range of about 0.1 Hr⁻¹ toabout 300 Hr⁻¹, more preferably in the range of about 1.0 Hr⁻¹ to about250 Hr⁻¹, and most preferably in the range of about 10 Hr⁻¹ to about 100Hr⁻¹. Pressure in the contact zone may be from 0.1 to 30 atm. absolute,preferably 1 to 3 atm. absolute, most preferably about 1 atm. absolute.The catalyst may be contacted in any reaction zone such as a fixed bed,a moving bed, a slurry, a transfer line, a riser reactor or a fluidizedbed.

[0017] Test Conditions

[0018] A series of runs in a small bench reactor was conducted on hexeneas a model compound. Comparison runs with a ZSM-5 zeolite catalystcommercially available from Intercat. Inc., of Sea Girt, N.J. wereconducted over a fixed bed of catalyst. The effluent stream was analyzedby on-line gas chromatography. A column having a length of 60 m packedwith fused silica was used for the analysis. The gas chromatograph was adual flame ionization detector equipped Hewlett-Packard Model 5880. Alltabulated data is in weight percent unless otherwise indicated.

EXAMPLE 1 Constant Reactor Conditions

[0019] The hexene model compound was cracked over ZSM-5, SAPO-11 andSAPO-34 catalysts at 650° C., 12 hr⁻¹ WHSV, 1.6 nitrogen dilution, 12psig. TABLE 1 Catalyst ZSM-5 SAPO-34 SAPO-11 Conversion 95.4 63.6 88.8Key Results Ethylene 24.5 11.0 8.4 Propylene 35.8 30.3 54.8 Butylenes12.8 11.2 11.8 Aromatics 12.8 2.7 8.5 Light Saturates 9.5 8.5 5.4Selectivity (% of Conversion) Ethylene 25.7 17.3 9.5 Propylene 37.5 47.661.7 Butylene 13.4 17.6 13.3 Propylene/ethylene 1.5 2.8 6.5Propylene/butylene 2.8 2.7 4.7

[0020] As can be seen from Table 1, the SAPO-11 catalyst was slightlyless active than the comparison ZSM-5 in terms of conversion. The datashow that SAPO-11 was more selective for propylene over ethylene andbutylene as ZSM-5, and SAPO-34 also shows significantly increasedproduction of propylene over both ethylene and butylene.

EXAMPLE 2 Constant Conversion

[0021] In this example the conditions are the same as in Example 1except the weight hourly space velocity was adjusted to make conversionequal for the control ZSM-5 and SAPO-11. TABLE 2 Catalyst ZSM-5 SAPO-11WHSV, Hr⁻¹ 40 12 Conversion 89.0 88.8 Key Results Ethylene 13.1 8.4Propylene 47.6 54.8 Butylene 14.9 11.8 Aromatics 7.4 8.5 Light Saturates6.1 5.4 Selectivity Ethylene 14.7 9.5 Propylene 53.3 61.7 Butylene 16.713.3 Propylene/Ethylene Ratio 3.6 6.5 Propylene/Butylene Ratio 3.2 4.7

[0022] As can be seen from Table 2, SAPO-11 produced significantly morepropylene and less ethylene and butylenes than ZSM-5 catalyst.

EXAMPLE 3 Effect of Temperature and Throughput

[0023] In this example SAPO-11 extrudate catalyst was tested with thehexene model compound in the apparatus of Example 1 under the conditionsindicated in Table 3. TABLE 3 Temperature, ° C. 650 600 600 WHSV, Hr⁻¹12 12 8 Conversion 88.8 75.9 87.9 Key Results Ethylene 8.4 3.6 3.9Propylene 54.8 60.6 69.7 Butylene 11.8 7.1 7.4 Aromatics 8.5 2.7 5.0Light Saturates 5.4 1.8 2.0 Selectivity, % Ethylene 9.5 4.7 4.4Propylene 61.7 79.8 79.3 Butylene 13.3 9.4 8.4 Propylene/Ethylene Ratio6.5 16.8 17.9 Propylene/Butylene Ratio 4.7 8.5 9.4

[0024] As the data above indicate, selectivity is improved by reducingthe temperature and by maintaining high conversion by decreasingthroughput thus increasing the average time the feedstock is in contactwith the catalyst. The propylene/ethylene ratio approaching 18:1 isexceptional, as is the propylene/butylene ratio at 9.4:1. With ZSM-5catalysts lowering the temperature typically results in increasingbutylene selectivity, while the SAPO catalysts display the oppositetread which is unexpected. It has been found that the selectivity of thecatalysts can be maintained over a wide range of conversion levels solong as cracking conditions are maintained.

EXAMPLE 4 Selectivity in Cracking of a Typical Refinery Feedstock

[0025] A typical refinery feedstock, Baton Rouge Light Cat. Naphtha,(LCN) was contacted with fresh and steamed SAPO-11 at 600° C., 6 Hr⁻¹WHSV, 1.6 N₂ dilution, and 12 psig. The results are listed in Table 4.TABLE 4 Catalyst ZSM-5 SAPO-11 SAPO-11 Presteaming Conditions 816° C./40Hr. Fresh 593° C./16 Hr. Conversion 40.7 33.9 33.2 Key Results Ethylene5.1 3.2 2.6 Propylene 24.7 24.9 25.3 Butylene 9.5 4.2 3.8 Aromatics 4.55.5 4.4 Light Saturates 1.4 1.6 1.5 Selectivity, % Ethylene 12.5 9.4 7.8Propylene 60.7 73.5 76.2 Butylenes 23.3 12.4 11.4 Propylene/EthyleneRatio 4.8 7.8 9.7 Propylene/Butylene Ratio 2.6 5.9 6.6

[0026] The selectivity observed with the model compound is maintainedwith the refinery feedstock. Selectivity appears to improve when thecatalyst is presteamed.

EXAMPLE 5 Performance of Calcium exchanged SAPO-11

[0027] To 10 g SAPO-11 was added 1000 ml of a 10 wt % Ca(NO₃)₂ solution.This solution was stirred for 16 hrs at 65° C. After washing, the samplewas dried overnight at 90° C., followed by air calcination for 16 hrs at525° C. The procedure was repeated twice to obtain the finishedcatalyst. The calcium exchanged SAPO-11 was contacted with the hexenemodel compound at 600° C., and 2 Hr⁻¹. The nitrogen diluent tohydrocarbon ratio was 5:1. The results are shown in Table 5. TABLE 5Catalyst ZSM-5 SAPO-11 Conversion 99.3 89.8 Key Results Ethylene 20.44.3 Propylene 22.6 57.5 Butylenes 8.3 11.8 Aromatics 25.0 1.4Selectivity, % Ethylene 20.5 4.8 Propylene 22.8 64.0 Butylenes 8.4 13.1Propylene/Ethylene Ratio 1.1 13.4 Propylene/Butylene Ratio 2.7 2.9

[0028] As demonstrated by the data above Ca SAPO-11 was found to be veryselective for propylene with a propylene selectivity of 64% and lowproduction of both ethylene and butylenes. An additional benefit is thelow aromatics production of only 1.4%

EXAMPLE 6 Improved Stability with Rare Earth Treated NonzeoliticCatalyst

[0029] SAPO-11 treated with a rare earth (lanthanum) resists loss ofactivity when subjected to prolonged exposure to steam. Most zeolite andother molecular sieve catalysts display a characteristic loss ofactivity when exposed to steam over a prolonged period. As the databelow demonstrate rare earth treatment of catalyst (SAPO-11) produces acatalyst with 60-70% improvement in catalyst activity relative tonon-treated SAPO-11 while retaining the outstanding selectivity forpropylene over both ethylene and butylene observed in the examplesabove. A sample of SAPO-11 was ion-exchanged with a lanthanum solutionby suspending 10 grams of SAPO-11 in 100 grams of water and 5 grams ofLaCl₃.6 H₂O were added. The mixture was refluxed at 100° C. for 4 hrs,then dried and calcined.

[0030] The exchanged catalyst was contacted with Baton Rouge Light CatNaphtha, at 500° C., 1/1 steam to hydrocarbon weight ratio, at 5 Hr⁻¹,12 psig in the apparatus of Example 1. The steamed catalysts weretreated at 760° C. with 100% steam for 16 hours prior to the crackingtest. The results are shown in Table 6 below. TABLE 6 Catalyst FreshSteamed SAPO- Steamed SAPO-11 11 LaSAPO- 11 Conversion 27.5 12.0 20.2Key Results Ethylene 1.5 0.4 0.9 Propylene 23.1 10.0 17.0 Butylene 2.71.5 2.1 Aromatics 2.9 2.1 2.7 Light Saturates Selectivity, % Ethylene5.5 3.3 4.4 Propylene 84.0 83.1 84.0 Butylene 9.8 12.5 10.4Propylene/Ethylene Ratio 15.2 25.2 19.1 Propylene/Butylenes Ratio 8.56.6 8.1

[0031] The preceding data show a positive result of rare earth treatmentof a SAPO catalyst. The improved resistance to loss of activity onexposure to steam allows prolonged use of the catalyst. The foregoingresults are provided to illustrate the operation of the invention insome of its embodiments. The examples are provided by way ofillustration and not as limitations on the scope or practice of theinvention, which is defined and limited by the following claims.

We claim:
 1. A method of converting an olefinic hydrocarbon feedstock toa high propylene content product comprising: contacting a hydrocarbonfeedstock under catalytic cracking conditions with a catalyst comprisinga catalyst selected from the group consisting of SAPO catalysts, MeAPOcatalysts, MeASPO catalysts, ElAPO catalysts and ElASPO catalysts, undercracking conditions to selectively produce propylene.
 2. The method ofclaim 1 wherein the selectivity produces a propylene to butylene ratioof at least 2:1 or a propylene to ethylene of at least 4:1.
 3. Themethod of claim 1 wherein the olefinic hydrocarbon feedstock consistsessentially of hydrocarbons boiling within the range of 18° to 220° C.(65° F. to 430° F.).
 4. The method of claim 1 wherein the olefinichydrocarbon feedstock consists essentially of hydrocarbons boiling inthe range of 18° to 148° C. (65° F. to 300° F.).
 5. The method of claim1 wherein the olefinic hydrocarbon feedstock comprises from about 10 wt% to about 70 wt % olefins.
 6. The method of claim 1 wherein theolefinic hydrocarbon feedstock comprises from 20 wt % to 70 wt %olefins.
 7. The method of claim 1 wherein the olefinic hydrocarbonfeedstock comprises from about 5 wt % to about 35 wt % paraffins.
 8. Themethod of claim 1 wherein the olefinic hydrocarbon feedstock comprisesfrom about 10 wt % to about 30 wt % paraffins.
 9. The method of claim 1wherein the olefinic hydrocarbon feedstock comprises from about 10 wt %to about 25 wt % paraffins.
 10. The method of claim 1 wherein thecatalyst is contacted in the range of 400° C. to 700°.
 11. The method ofclaim 1 wherein the catalyst is contacted at a WHSV of 1 to 300 hr⁻¹.12. The method of claim 1 wherein the catalyst is contacted at apressure of 0.1 to 30 atm. absolute.
 13. The method of claim 1 whereinthe catalyst comprises a catalyst selected from the group consisting ofSAPO-11, SAPO-17, SAPO-31, SAPO-34, SAPO-35, SAPO-41, SAPO-44, MeAPO-11,MeAPO-31, MeAPO-41, MeAPSO-11, MeASPO-31, MeASPO-41, MeASPO-46,ElAPO-11, ElAPO-31, ElAPO-41, ElAPSO-11, ElAPSO-31 and ElASPO-41. 14.The method of claim 1 wherein the catalyst is prepared by a method whichcomprises ion exchanging the catalyst with a solution comprising analkaline earth metal ion or a rare earth metal ion.
 15. The method ofclaim 1 wherein the catalyst is exchanged against a solution comprisinga rare earth metal ion selected from the group consisting of cerium,lanthanum, praseodymium, neodymium, promethium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,lutetium and mixtures thereof
 16. The method of claim 9 wherein the rareearth metal ion comprises lanthanum.
 17. The method in claim 1 whereinthe hydrocarbon feed is cracked over the catalyst at reactortemperatures of from about 400-700° C., pressures of from about 0.1atmosphere to about 30 atmospheres absolute, and weight hourly spacevelocities of from about 0.1 hr⁻¹ to about 100 hr⁻¹.
 18. In a method forcatalytic cracking of an olefinic hydrocarbon feed to produce a lightolefin containing product, the improvement which comprises mixing acatalyst selected from the non zeolitic catalyst group consisting ofSAPO catalysts, MeAPO catalysts, MeASPO catalysts, ElAPO catalysts andElASPO catalysts with a second cracking catalyst in a quantitysufficient to increase propylene content in the light olefin productwhile decreasing either ethylene or butylene when the productcomposition obtained with the mixed catalyst is compared to the productcomposition obtained with the second catalyst alone under the samereaction conditions.
 19. The method of claim 18 wherein the olefinichydrocarbon feedstock consists essentially of hydrocarbons boilingwithin the range of 18° to 220° C. (65° F. to 430° F.).
 20. The methodof claim 18 wherein the olefinic hydrocarbon feedstock consistsessentially of hydrocarbons boiling in the range of 18° to 148° C. (65°F. to 300° F.).
 21. The method of claim 18 wherein the olefinichydrocarbon feedstock comprises from about 10 wt % to about 70 wt %olefins.
 22. The method of claim 18 wherein the olefinic hydrocarbonfeedstock comprises from 20 wt % to 70 wt % olefins.
 23. The method ofclaim 18 wherein the olefinic hydrocarbon feedstock comprises from about5 wt % to about 35 wt % paraffins.
 24. The method of claim 18 whereinthe olefinic hydrocarbon feedstock comprises from about 10 wt % to about30 wt % paraffins.
 25. The method of claim 18 wherein the olefinichydrocarbon feedstock comprises from about 10 wt % to about 25 wt %paraffins.
 26. The method of claim 18 wherein the selected catalystcomprises a silicoaluminophosphate selected from the group consisting ofSAPO-11, SAPO-17, SAPO-31, SAPO-34, SAPO-35, SAPO-41, SAPO-44, MeAPO-11,MeAPO-31, MeAPO-41, MeAPSO-11, MeAPSO-31, MeAPSO-41, MeAPSO-46,ElAPO-11, ElAPO-31, ElAPO-41, ElAPSO-11, ElAPSO-31, and ElAPSO-41. 27.The method of claim 18 wherein the mixed catalyst is contacted in therange of 400° C. to 700° C.
 28. The method of claim 18 wherein thecatalyst is contacted at a WHSV of 1 hr⁻¹ to 300 hr⁻¹.
 29. The method ofclaim 18 wherein the catalyst is contacted at a pressure of 0.1 to 30atm.
 30. The method of claim 18 wherein the selected catalyst isprepared by a method which comprises ion exchanging the catalyst with anaqueous solution comprising an alkaline earth metal ion or a rare earthmetal ion.
 31. The method of claim 30 wherein the selected catalyst isexchanged against a solution comprising a rare earth metal ion selectedfrom the group consisting of cerium, lanthanum, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium and mixtures thereof. 32.The method of claim 30 wherein the rare earth metal ion compriseslanthanum.
 33. The method in claim 18 wherein the hydrocarbon feed iscracked over the catalyst at reactor temperatures of from about 400-700°C., pressures of from about 0.1 atmosphere to about 30 atmospheresabsolute, and weight hourly space velocities of from about 0.1 hr⁻¹about 100 hr ⁻¹.
 34. A method for enhancing the stability of asilicoaluminophosphate catalyst in propylene production which comprisesion exchanging the selected catalyst with a solution which comprises arare earth metal.
 35. The method of claim 34 wherein the ion exchange iswith an aqueous solution comprising a rare earth metal ion.
 36. Themethod of claim 34 wherein the selected catalyst is exchanged against asolution comprising a rare earth metal ion selected from the groupconsisting of cerium, lanthanum, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium, lutetium and mixtures thereof.
 37. The method ofclaim 34 wherein the rare earth metal ion comprises lanthanum.
 38. Themethod of claim 22 wherein the catalyst is selected from the groupconsisting of SAPO catalysts, MeAPO catalysts, MeASPO catalysts, ElAPOcatalysts and ElASPO catalysts and mixtures thereof.
 39. A method forproducing propylene in a cracking process while minimizing production ofbutylene which comprises contacting an olefinic hydrocarbon feed with anon-zeolitic silicoaluminophosphate containing catalyst under crackingconditions to produce at least 2 times as much propylene as butylenes.40. A method according to claim 39 wherein the process produces at least4 times as much propylene as ethylene.
 41. A method according to claim39 wherein the catalyst is selected from the group consisting of SAPOcatalysts, MeAPO catalysts, MeASPO catalysts, ElAPO catalysts and ElASPOcatalysts and mixtures thereof.
 42. A method according to claim 41wherein the catalyst is a SAPO selected from the group consisting ofSAPO-11, SAPO-17, SAPO-31, SAPO-34, SAPO-35, SAPO-41, SAPO-44.
 43. Amethod according to claim 39 wherein at least 2.5 times as muchpropylene as butylenes is produced.
 44. A method according to claim 39wherein at least 3 times as much propylene as butylenes is produced. 45.A method for producing propylene in a cracking process while minimizingproduction of ethylene which comprises contacting an olefinichydrocarbon feed with a non-zeolitic silicoaluminophosphate containingcatalyst under cracking conditions to produce at least 2 times as muchpropylene as ethylene.
 46. A method according to claim 45 wherein theprocess produces at least 4 times as much propylene as ethylene.
 47. Amethod according to claim 45 wherein the catalyst is selected from thegroup consisting of SAPO catalysts, MeAPO catalysts, MeASPO catalysts,ElAPO catalysts and ElASPO catalysts and mixtures thereof.
 48. A methodaccording to claim 45 wherein the catalyst is a SAPO selected from thegroup consisting of SAPO-11, SAPO-17, SAPO-31, SAPO-34, SAPO-35,SAPO-41, SAPO-44.
 49. A method according to claim 45 herein at least 2times as much propylene as butylenes is produced.
 50. A method accordingto claim 45 wherein at least 3 times as much propylene as butylenes isproduced.